The present invention relates to a belt supporting and tracking apparatus. More particularly, it relates to an improved apparatus for controlling the lateral movement of a belt from its predetermined path.
The invention is particularly suited for use in an electronic device such as an electrostatographic printing machine. However, it should be appreciated that the apparatus could also be used in many other types of machines which utilize a moving belt.
In electrostatographic printing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
Many commercial applications of the above process employ a photoconductive insulating member in the form of a belt which is supported about a predetermined path past a plurality of processing stations to ultimately form a reproduced image on copy paper. The location of the latent image recorded on the photoconductive belt must be precisely defined in order to have the various processing stations acting thereon optimize copy quality. To this end, it is critical that the lateral alignment of the photoconductive belt be controlled within prescribed tolerances. Only in this manner will a photoconductive belt move through a predetermined path so that the processing stations disposed thereabout will be located precisely relative to the latent image recorded thereon. Lateral movement of the photoconductive belt is particularly a problem in connection with color copiers where the precise tracking of the belt is mandatory for acceptable copy quality.
When considering control of the lateral movement of the belt, it is well known that if the belt were perfectly constructed and entrained about perfectly cylindrical rollers mounted and secured in an exactly parallel relationship with one another, there would be no lateral movement of the belt. In actual practice, however, this is not feasible. Due to the imperfections in the system's geometry, the belt velocity vector is not normal to the roller axis of the rotation, and the belt will move laterally relative to a roller until reaching a kinematically stable position.
Existing methods of controlling the lateral movement of a belt comprise servo systems, crowned rollers and flanged rollers. Servo systems use steering rollers to maintain lateral control of the belt. While they generally apply less stress to the sides of the belt than do crowned rollers and flanged rollers, servo systems are frequently rather complex and costly. Crowned and flanged rollers while being inexpensive, frequently produce high local stresses resulting in damage to the edges of the belt.
Accordingly, it has been considered desirable to develop a new and improved edge guide system for belt tracking which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.